In certain mining operations, dual passage drill strings are employed to drill shafts. A rolling cutter bit is mounted to the drill string. A circulating fluid, typically air, is pumped down the annulus of the drill string and out nozzles. The air returns up a central passage along with cuttings. The nozzles are circular cross section jets mounted between each bit leg. An advantage of a dual passage drill string is that drilling fluid is circulated through conduits of fixed uniform cross-section to produce cutting recovery, cooling and lubrication of the drill bit. It is important to direct a fluid flow across the roller cutters of a bit to cool the cutters and to prevent materials from building up on the cutters. While successful, improvements in the delivery of air across the cutters is desired.